Rate

40-60

Regularity

Regular

P waves

Inverted, if present

PRI

< 0.12, if P waves are even visible

QRS

0.08-0.12

Rate

60-100

Regularity

Slightly irregular

P waves

Bizarre/unusual

PRI

< 0.20

QRS

0.08-0.12

Rate

60-100

Regularity

Irregular

P waves

Morphology changes

PRI

Changes

QRS

0.08-0.12